Their findings further implied that the transformation tropism of these PTLVs (i.e., CD4+ T-cells for HTLV-1 and CD8+ T-cells for HTLV-2) is driven by the clonal expansion and selection of a transformed proviral cellular clone over a latency period of several decades, as occurs in HTLV-1+ ATLL patients [15]. Here, CD4 is linked to adult T-cell leukemia/lymphoma.